BK47-3/4" ID Bore Cast iron Pulley - 4.45" OD for V-belts 4L, 5L (BK4734)1 Groove BK47 3 4" ID 3 4" Bore cast iron Solid Pulley with 4. 45" inch OD for V belts size 4L, 5L (BK4734) BK Finished Bore Sheaves for (4L or A or 5L or B Belts) BK Sheaves are accurately machined from fine grained cast iron, statically balanced, They are furbished with Standard Keyseats and Hollow Head Setscrews The V Belts you that can run in this pulley are 4L, or A or 5L, B, V Belts. The belt series most common for this pulley is the 4L and A